In general, window chain assemblies comprise links fastened to one another by rivets. The links are usually stamped out utilizing conventional metal stamping techniques after which several necessary secondary operations are required to produce a finished link. The blanks, from which the rivets are made, are usually formed by wire drawing techniques. Examples of conventional methods for fabricating chains of various types can be found in U.S. Pat. Nos. 1,873,619, 3,125,850, 3,370,416 and 4,037,403.
However, the above-mentioned U.S. patents have not specifically or indirectly addressed the unique problems arising in the construction of chains employed in skylight window operators.
In particular, U.S. Pat. No. 4,521,993 to Tacheny et al discloses a chain operator for a window, especially designed for a skylight window. Chain operators of this general type include a chain assembly constructed from a plurality of solid links and a plurality of U-shaped links with the U-shaped links being positioned in an end-to-end abutting relation, and the solid links having a thickness to closely fit within the U-shaped links. In this general application where the chain assembly of the window operator is designed to push the window unit under compression rather than pull it under tension the chain links must be constructed to provide substantial rigidity for the chain when it is in a straight configuration, so that the chain can transmit force to the swinging window unit for opening and closing thereof. The chain must also possess the requisite degree of lateral flexure to conform to the arcuate path traversed by swinging window unit from the window liner.
In prior art skylight chain constructions, it has thus become customary for the links thereof to have co-acting shapes to facilitate movement of the chain between straight and curved configurations, while maximizing the strength thereof. Also, for increased strength, the rivets have been provided with large heads pivotally interconnecting the opposite ends of a solid link and a pair of U-shaped links.
Therefore, in order to ensure that the finished chain assembly has (i) a high degree of structural rectilinearity in its extended configuration, as well as (ii) possesses the requisite degree of lateral flexure to conform to the arcuate path traversed by a swinging window unit from the window liner window operator chain assemblies require extremely high tolerances. However, with conventionally stamped links, there are several inherent limitations in the process thereof which provide links with specifications falling outside acceptable tolerances required by window operator chain assemblies. Specifically, the links produced from conventional stamping methods have associated therewith, tapers (i.e., edges) with die breaks up to 30.degree., corner tears, waves, poor surface quality and break out, in addition to not being highly planar. Also using conventional stamping techniques, any additional structural features that a link must have for a particular chain assembly design must be produced by additional operations. As with the blanks produced from conventional wire drawing techniques high tolerances on the order of 0.001 inch in length are typically not achievable.
In constructing a chain assembly for use in a window operator as hereinbefore described, the requirement of high tolerance in the dimension of the parts cannot be overemphasized, since the chain assembly usually requires the assemblage of fifty or more links with rivets formed from blanks, and the resulting or total error of the final chain assembly is the sum of all the errors in the dimensions of the comprising components. Thus, if the tolerances of each of the individual components are not maintained within a high degree of accuracy, then a resultant chain assembly cannot satisfy the following criterion: (i) that resultant chain assembly be sufficiently rigid and rectilinear along its longitudinal dimension when in its extended configuration, and (ii) that it possess sufficient lateral flexure as to conform to the arcuate traverse of the swinging window unit from the liner to which the swinging window unit is mounted.
While the prior art has addressed the problem associated with inadequately configured chain assemblies with respect to criterion (i) and (ii) discussed hereabove, the solutions thereto have been wholly inadequate for purposes of obtaining the objects of the present invention. Therefore, conventional chain construction techniques have been retained and post assembly corrective measures have been developed to compensate for the inherent shortcomings of conventional chain construction methods. Such conventional chain construction techniques involve the intentional introduction of "error" in each link such that the assembled chain assembly possesses a predetermined degree of arcuate curvature, after which corrective measures are taken. The principal technique used to correct the shape of an assembled chain for a window operator has been to use jaw-like apparatus to "overbend" completely assembled chains having predetermined arcuate curvature to thereby correct its shape as to satisfy criterion (i) and (ii) hereabove, but this operation results of course, in loosening or tightening the component parts and preventing the establishment of precise interrelationships therebetween. Moreover, since resultant chain assemblies will not require the same degree of overbending to correct their shapes, this method more often than not produces chain assemblies which fail to meet criterion (i) and (ii) as desired. One important consequence of this overtightening and loosening of rivets is that this renders the chain assembly extremely stiff at locations along the chain length which prevents the same from turning about the drive sprocket of a chain operator. Often, this resistance of the chain to turn about the drive sprocket, causes the chain operator to fail.
As important however, chains made from stainless steel and other metals desired for their non-corrosive properties, cannot be subjected to such overbending procedures to correct the shape of a chain assembly produced from components of low tolerance, as stainless steel and like metals will shear and fracture when subjected to forces associated with overbending procedures. This fact has thus prevented the fabrication of skylight chains from highly desired materials such as stainless steel, and other metals desired for their non-corrosive properties. As a result of this fact, prior art chain assemblies for chain operators have resorted to the use of "mild" steel to fabricate the link plates of chain assemblies. In order to provide a non-corrosive outer coating to the mild steel links, barrel plating processes are typically employed. However, even with the finest plating processes and equipment, uneven plating of link plates occurs, the result of which is premature wearing away of deposited non-corrosive coatings. This renders link plates so exposed susceptible to oxidation and corrosion thereby reducing the quality of appearance and performance of such chain assemblies, and operators employing the same.
Therefore, there is a great need in the art for chain assemblies made of non-corrosive materials, which do not require plating, and which, such as stainless steel, can be used with chain operators for windows.
In view of the above-recognized problems and the prior art solutions thereto, it therefore becomes a primary object of the present invention to provide a method for making chain assemblies for window and like operators, which possess structural features of substantial rectilinearity along its longitudinal dimension when in its extended configuration, and sufficient lateral flexure for conforming to the arcuate traverse of a swinging window unit from its liner.
It is also an object of the present invention to provide a method for making a chain assembly for a window operator, wherein the links and rivets thereof are made of stainless steel, thereby eliminating the requirement of plating link plates with non-corrosive coatings.
It is a further object of the present invention to provide such a method wherein the chain assembly is precision-formed from links and rivets having ultra-high tolerances, as to produce chain assemblies therefrom having the desired degree of longitudinal rectilinearity when extended, and the required lateral flexure to conform to arcuate geometry, without utilizing "overbending" and similar shape-corrective measures.
It is a further object of the present invention to provide such a method utilizing fine blanking metal working principles to form the links of the chain assembly, and a combined "orbital" riveting method and "spinning method" for forming the heads of the rivets which hold the links together.
It is a further object of the present invention to provide such method for making a chain assembly which uses only one type of link to be used in forming the chain assembly.
It is an even further object of the present invention to provide such a method which is capable of mass producing high tolerance chain assemblies at a low cost.
It is an even further object of the present invention to provide such method which is readily adaptable to automated mass production of chain assemblies in accordance with the principles of the present invention.
It is a further object of the present invention to provide a chain assembly produced by such method.
It is an even further object of the present invention to provide a method for making chain assemblies for window operators, which eliminates the requirement of secondary operations such as "overbending" procedures performed on chain assemblies.